Technical Abstract:
In Iowa row-crop agriculture and grazing have altered the hydrologic cycle causing greater volumes of water to reach streams in shorter times, accelerating stream incision and bank erosion. Row-crop plants and pasture grasses also have much shallower roots providing less reinforcement to stream banks than native vegetation. Stream bank erosion can account for >50% of the sediment in streams, the major nonpoint source pollutant in Iowa. In this project the impacts of row cropping and different cattle grazing practices on bank erosion are being compared to stream reaches with riparian forests and grass filters (the controls). Continuous, rotational and intensive rotational grazing practices are being studied. Rotational and intensive rotational systems consist of numerous paddocks that provide pastures with rest time between grazing events that should lead to more stable stream banks. Erosion pins, measured every season except winter, are being used to estimate the stream bank erosion rate. Surveying the height and length of the eroding sites of each treatment reach is used to estimate the stream eroding areas. Preliminary results show that the controls have the least bank erosion and row-crops the most, but the grazing practices do not follow the expected trend. There is no consistent difference between the grazing treatments suggesting that livestock access to stream banks contributes to stream bank instability.